Use docker image debian-bullseye-erlang instead of debian-buster-erlang

Let's use newer debian to avoid problems with older erlang. Furthermore,
the new image builds rebar3 to avoid issues with unmatching erlang
versions.

Change-Id: I7b1956c515daccf6ab1ff87031c6fec649cadb4b

jobs/gerrit-verifications.yml

@@ -41,7 +41,7 @@
               -v "$PWD:/build" \
               -v "$ARTIFACT_STORE:/artifact_store" \
     docker_img: '$USER/debian-stretch-jenkins'
-    docker_img_erlang: '$USER/debian-buster-erlang'
+    docker_img_erlang: '$USER/debian-bullseye-erlang'
     timeout_cmd: '/usr/bin/timeout 30m'
     cmd: '{docker_run} {docker_img} {timeout_cmd} /build/contrib/jenkins.sh'
     gerrit_url: 'ssh://jenkins@gerrit.osmocom.org:29418'

scripts/osmo-ci-docker-rebuild.sh

@@ -5,7 +5,7 @@ cd "$(dirname "$0")/.."
 docker_images_require \
 	"debian-stretch-jenkins" \
 	"debian-buster-jenkins" \
-	"debian-buster-erlang" \
+	"debian-bullseye-erlang" \
 
 if [ "$(arch)" = "x86_64" ]; then
 	docker_images_require \